1. Field of the Invention
The present invention relates to an alarm system for a vehicle, especially to an alarm system capable of determining a relative position of a vehicle corresponding to an object and a distance between the vehicle and the object.
2. Description of the Prior Art
As vehicles become more prevalent, drivers are demanding higher and higher standards of safety and comfort. In the past, a rearview mirror and side mirrors are installed to reduce the possibility of car crashes in order to prolong the life of a car. However, these mirrors cannot reflect the actual distance between the car and other vehicles nearby. For example, the side mirrors tend to reduce the size of nearby vehicles by a scale greater than it should be. Thus the driver often has to rely on his instinct and his experience to determine how far the nearby vehicles are. Occasionally the car may collide onto another object when the car is reversing and turning because the driver misjudges the distance between the car and the object. Moreover, there are blind spots which cannot be detected by either the rearview mirror or the side mirrors, so the mirrors are not able to satisfy the basic safety demand. Thanks to the parking distance control system because it can alert the driver when the car is getting too close to another still object. When the car is getting very close to another object, the parking distance control system will beep. Thus the driver would be alerted to pay extra attention when he steers his car.
Presently the parking distance control system mainly utilizes the feedback of ultra sound waves. By calculating the time interval between generating the ultra sound waves and receiving the ultra sound waves, a distance between a vehicle and an object can be derived. However the ultra sound waves greatly decay in the air, they can only be used to detect the presence of other objects very close to the car. Thus the parking distance control system cannot be used to detect objects far away from the vehicle. In the prior art, U.S. Pat. No. 4,552,456 discloses utilizing time differences between emitting and receiving of short waves in many photoelectric components to calculate a distance between cars, however this is costly and is unable to detect if other vehicles have moved into a warning region. U.S. Pat. No. 5,283,622 discloses utilizing the intensity of the reflected light to determine a distance between cars, however the environment often affects the intensity of the reflected light. Thus it is not a suitable collision proof device. Moreover, it cannot be used to detect if other vehicles have moved into a warning region. Lastly U.S. Pat. No. 5,594,413 discloses a method for measuring the distance between cars, but it is also unable to detect if other vehicles have moved into a warning region.